1. Field of the Invention
The present invention relates to a hydraulic clamp adapted to clamp a member to be clamped or fixed such as a metal mold, a work plate and the like onto a fixed annular table of an injection molding machine, a machine center and so on, and more specifically to a hydraulic clamp of the type including a hydraulically operated piston actuated along an axis declining in a forward direction to directly engage and clamp a member to be clamped.
2. Description of Prior Art
Such a hydraulic clamp is generally described in Japanese Patent laid open Publication No. 1981-163854.
As shown in FIGS. 9 and 10, the basic construction described in the known system is as follows.
Specifically, a cylinder bore 108 is formed in a housing 105 of a hydraulic clamp 104 so that the bore declines in a forward direction and a piston 109 is inserted in fluid tight relation into said cylinder bore 108 so as to be movable forward and backward therein.
A clamping member 112 is disposed on the forward side of the piston 109, and said clamping member 112 is interlockingly connected to the piston 109 so as to be movable together therewith.
A clamping actuation hydraulic chamber 114 is formed in the cylinder bore 108 behind said piston 109.
When the piston 109 is retracted, the clamping member 112 is in the unclamped state, whereat the clamping member 112 is retracted to an unclamped position rearwardly towards the back and upper side of the cylinder bore. When the piston 109 is actuated forwardly by the hydraulic pressure admitted to the clamping actuation hydraulic chamber 114 the clamping member 112 is advanced to a clamping position X toward a forward and lower side so as to assume a clamping state at which a fixed portion 102a of a metal mold 102 (clamped member D) in the front of the housing 105 is fixedly clamped by the clamping member 112 from above.
In the above basic known construction, conventionally a guide hole 110 of a smaller diameter than that of the cylinder bore 108 was coaxially formed through the front lower portion of the cylinder bore 108. A piston rod 111 was inserted into the guide hole 110, and the back portion thereof was fixed to the piston 109 and the clamping member 112 was provided in the front portion of piston rod 111.
The following problems are associated with the above mentioned prior art construction.
a) Working accuracy of a process machine is low. PA0 b) The service life of the hydraulic clamp is short. PA0 c) The clamped area of the clamped member is apt to be damaged. PA0 a) Accuracy of the processing machine can be enhanced PA0 b) The service life of the hydraulic clamp becomes longer PA0 c) Damage to the clamped member can be prevented.
Since a piston rod 111 inherently is smaller in outer diameter and in cross-sectional area, its bending ridigity is small. Accordingly, when a pulling-up impact such as a metal mold removing force and a work processing reaction force is imposed on the clamped member D when the member is fixedly clamped to the fixed angular table 101 of the process machine, the piston rod 111 and the clamping member 112 are elastically deformed by the reaction force, so that the fixed member D raises from the table 101 and working accuracy is correspondingly lowered by that pulled up portion. PA1 Since the piston rod 111 has a small diameter and a small cross-sectional area, and is subject to a large bending stress acting on it at the time of clamping, it is apt to become fatigued by an accumulated number of clamping operations and its fatigue life is shortened. Accordingly, the service life of the hydraulic clamp is short. PA1 Since the clamping member 112 is attached to the piston rod 111, which rod has a small diameter, the clamping surface of the clamping member 112 inherently is small. Therefore, the clamped area of member D is subjected to an intense localized surface pressure when being clamped and the clamped area 102(a) thereof is apt to become damaged. PA1 Since the directly protruding clamping member integrated with the piston can be manufactured with a large diameter and have a large cross-sectional area, its bending rigidity becomes larger. Therefore, even when a pulling up impact force is imposed on the clamped member, the upward elastic deformation of the clamping member will be small, the clamped member can be prevented from being lifted up and the processing accuracy can be enhanced. PA1 The clamping member, having a large cross-sectional area, is only subjected to a small bending stress at the time of clamping, and its fatigue life becomes longer. Therefore, the service life of the hydraulic clamp becomes longer. PA1 Since the clamping surface of the clamping member can be made to extend over a large area, the surface pressure exerted at the clamping area of the clamped member can be smaller and the damage to clamped area is prevented.